The present invention relates to a method and apparatus for analyzing the operability, or physical integrity, of a semiconductor integrated circuit by irradiating the semiconductor integrated circuit with a focused ion beam and detecting secondary electrons generated by the irradiation.
Japanese Patent Provisional Publication No. 142825/88 discloses one of the conventional methods for analyzing the operability of a semiconductor integrated circuit by irradiating the integrated circuit with a focused ion beam and detecting secondary electrons generated by the irradiation. This method is performed on an integrated circuit having wirings placed on a substrate, the wirings and the substrate being covered with a passivation film. A desired wiring is selected from among the substrate wirings and the selected wiring is irradiated with the focused ion beam in order to make holes in the passivation film and expose a predetermined portion of the wiring.
Next, while an area including the exposed portions of the wiring is irradiated with the focused ion beam, metal electrodes are formed around the holes by a CVD method using the focused ion beam. Then, the metal electrodes are irradiated with the focused ion beam, which causes secondary electrons to be released from the electrodes. The secondary electrons are detected and a potential waveform of the secondary electrons is measured in order to analyze the operation of the semiconductor integrated circuit.
The focused ion beam is deflected to perform a scanning movement during which the beam irradiates the specific area. Further, the CVD method using the focused ion beam refers to a method for making a film by the following steps: a desired portion is irradiated, while being scanned, with the focused ion beam, and at the same time, vapor of an organic compound is directed to the scanned portion; and then, part of the organic compound is adsorbed into the portion and is decomposed by the focused ion beam, and thereby forms the film. Generally in the process of forming electrodes, tungsten carbonyl is used as the organic compound vapor and metal electrodes of tungsten are formed.
However, in the conventional method, analyzing the operability of the semiconductor integrated circuit is often carried out by guessing fault points which cause a failure of the semiconductor integrated circuit and diagnosing a cause of the failure, or by tracing a cause if an unexpected mode of operation is observed. Moreover, a semiconductor integrated circuit to be analyzed for its operability is generally covered with a passivation film composed of an insulating film, so that the following steps are taken to analyze the operation of the semiconductor integrated circuit by detecting the secondary electrons generated by the irradiation of the focused ion beam:
selected portions of the wiring are exposed by making holes in the passivation film covering the wirings, and new electrodes are formed around the exposed portions of the wiring; and
then the electrodes are irradiated with the focused ion beam to analyze the operation of the semiconductor integrated circuit.
In the above case, a guess is made in advance as to the location of fault points and holes are made above or in the vicinity of the assumed fault points on the passivation film before irradiation with the focused ion beam for the purpose of analyzing the operation of the semiconductor integrated circuit. Therefore, if a failure of the circuit cannot be detected at the measurement points, it is necessary to make holes in other portions of the passivation film and analyze the operation again. In other words, the conventional method involves a trial and error approach which requires a substantial amount of work.